In a fuel pump described in JP-A-2000-193186 (corresponding to U.S. Pat. No. 6,053,208), fuel drawn into a pressurization chamber is pressurized and discharged by using a plunger that is held to be reciprocable in a cylinder of a housing.
In the fuel pump, a single plate metal diaphragm is located in a suction passage connected to the pressurization chamber, and is used as a damper mechanism for reducing a pressure pulsation of the fuel drawn from the suction passage to the pressurization chamber. When the pressure pulsation of the fuel generates and the fuel pressure increases, the diaphragm is elastically deformed by receiving the fuel pressure. For example, the diaphragm is deformed to the outside of the suction passage, so that the volume of the suction passage is increased. Thus, an increase of the fuel pressure in the suction passage can be restricted thereby reducing the vibration width of the pressure pulsation.
In a diaphragm device of a fuel pump described in JP-A-2005-042554 (corresponding to US 2007/0079810 A1), a metal diaphragm device is constructed by welding the whole peripheries of two metal diaphragms, and is fixed into a suction passage, in order to increase the reduction effect of the pressure pulsation.
In the diaphragm device of the fuel pump described in JP-A-2005-042554, a sealed space is formed by using the two metal diaphragms. In this case, when the pressure pulsation of fuel generates and the fuel pressure increases, the two metal diaphragms are elastically deformed at the same time by receiving the fuel pressure, and the diaphragm device is bent. Thus, an increase amount in the volume of the suction passage and the reduction effect of the pressure pulsation can be increased as compared with a fuel pump using a single metal diaphragm.
In the diaphragm device of JP-A-2005-042554, the sectional shapes of the two metal diaphragms are made uneven to be different from each other so that the two metal diaphragms have different characteristic frequencies. Accordingly, even when the frequency of the pressure pulsation is changed due to variation in a rotation speed of an engine and becomes to be equal to the characteristic frequency of one of the two metal diaphragms, the reduction effect of the pressure pulsation can be obtained on the other one of the two metal diaphragms.
However, because the two metal diaphragms having different uneven shapes in cross section are provided in the diaphragm device of the fuel pump, the product cost of the fuel pump is increased. The frequency of the pressure pulsation is changed in accordance with the engine type or the vehicle type to which the fuel pump is mounted. Therefore, it is necessary to prepare various kinds of the uneven metal diaphragms in accordance with the engine type and the vehicle type, thereby more increasing the product cost.